Food Preservation

Research Student: Connor Peebles

Background

Aflatoxin, a naturally-occurring toxic mold, is capable of causing health problems such as liver disease or cancer, autoimmune responses, digestive issues and in rare cases even death. High temperatures and humidity often result in a combination of molds that grow on decaying food, plants, grains and hay. This is of particular concern in many African countries where the quality control of food is less than in wealthy countries.

Our Goals

This specific project is focused on using desiccants such as CaCl2 to keep food dry. In order to reuse the desiccants, they need to be dehydrated so they can be reused for stored food products in high temperature and humidity areas. We attempt to do this using low power (and low cost) solar panels

Contributors 

This work is part of our research toward radically inexpensive solar electricity. Please meet our research team. Additionally, this work has been addressed by group projects in Schwartz’s Appropriate Technology Classes in Spring of 2018 and Spring of 2017.

Collaborator Mark Manary is a known pioneer in treating severely malnourished children through The Peanut Butter Project.

Previous Research

This project follows an experiment that used CaCl2 as a desiccant in a simulated 100% humidity environment which contained storage units of flour with varying amounts of CaCl2. Their Research found CaClto be an effective desiccant.

Research Summary: We investigated three desiccants: Calcium Chloride (CaCl2), Calcium Sulphate (CaSO4), and silica beads (beads of silica gel, or amorphous silicon dioxide, SiO2), comparing their ability to keep flour dry as well as be recharged by heating in an oven. While CaCl2 is the strongest (and cheapest) desiccant, it is difficult to recharge through heating, and is so far recommended for one time use only. For a reusable desiccant, we recommend silica beads for being the next best desiccant and the easiest to recharge. 

Desiccating Ability: A sealed container with water in the bottom provided a 100% relative humidity environment. In this container we placed sealed plastic bags of flour and some of the bags also had desiccant in them. The bags of flour were opened for about an hour at at time and then resealed. The relative humidity of these bags are displayed below.

Relative humidity as a function of time over 3 days. The “flour only” and Calcium Chloride data were taken simultaneously. The Calcium Sulphate and Silica Gel data were taken together in a different experimental run. More details are discussed here.

Recharging Desiccant: 

At the following website, we describe how we made an insulated, diode-heated oven powered by a solar panel to test the oven’s ability to recharge the desiccants.

Results of Recharging Efforts

While our desiccant recharging experiments are described in more detail on a separate website, we can summarize the results. We were not able to recharge CaCl2 as a desiccant. Hydrated CaCl2 is a liquid that leaks from the porous container. This liquid was heated to higher temperatures, driving away HCl and H2O, leaving CaO, a dry, white salt. Calcium chloride is a great desiccant, so much so that it will eventually absorb so much moisture that it just liquefies into a solution (CaCl2(H2O)). If one were to heat this solution to drive off all the water, they would get hydrochloric acid as a gas and a block of calcium oxide. Calcium oxide is also a desiccant but not commonly used as such.

Silica gel pellets are very common as a desiccant and that is because, even though it is more expensive than CaCl2, silica gel does not lower the humidity as low as CaCl2 does, does not turn into a solution with water and it is easier to dehydrate.

Further research will be done on this same set up but with silica gel pellets and calcium sulfate.

In conclusion, in terms of reusable desiccants it is between silica gel and SaSO4, silica gel can be dehydrated using solar energy and our small diode oven well SaSO4 can be dehydrated by simply setting it in a cook fire.

More research can be done as to how many times these desiccants can be re-used, if they are as effective after being dehydrated, and cost-benefit analysis as to if the desiccants that are able to be dehydrated are worth the initial investments.